Foot ailments are among the most common types of human suffering. The foot is required to support and move significant amounts of weight upon a very small surface area, which necessarily requires flexibility and adaptability. Accordingly, foot ailments may evolve into significant problems and be attendant with great pain. Among these foot ailments are interdigital neuritis and compression neuritis.
Interdigital neuritis or neuroma, more commonly known as Morton's neuroma or “foot neuroma,” is a common disease entity of the foot. Neuroma pain can range from mild to severe and typically presents as numbness, burning, tingling or sharp, shooting pain in the ball of the foot or between the toes. In severe cases the pain can be debilitating to the point that a person does not want to walk or even put their foot down. Women are more likely than men to experience this condition.
Tarsal tunnel syndrome arises from the compression of the posterior tibial nerve that produces symptoms along the nerve running from the medial aspect of the ankle down to the foot. The tarsal tunnel is a narrow space at the medial aspect of the ankle. The structures contained within the tunnel are the tibialis posterior tendon, flexor digitorum longus tendon, posterior tibial artery, posterior tibial vein, posterior tibial nerve and flexor hallucis longus muscle covered by flexor retinaculum. Symptoms arise due to compression of these structures within the tarsal tunnel specifically the posterior tibial nerve. An enlarged or abnormal structure that occupies space within the tunnel can compress the nerve for example an engorged or bounding artery. Also an injury, such as an ankle sprain, may produce inflammation and swelling in or near the tunnel, resulting in compression of the nerve. Symptoms of tarsal tunnel syndrome include painful burning, tingling, or numb sensations around the ankle and toes that becomes worse after standing for long periods of time. Pain is worse with activity and is relieved by rest. There can be “electric shock sensations” radiating up into the leg and down into the arch, heel, and toes. There can be hot and cold sensations in the feet and “pins and needles”-type feeling with increased sensation on the feet. Sometimes symptoms occur suddenly, often brought on or aggravated by overuse of the foot, such as prolonged standing, walking, exercising, or beginning a new exercise program. Early treatment of tarsal tunnel syndrome is important because left untreated, the condition may progress and can result in permanent nerve damage in the nerve compression is significant over a long period of time.
Current treatment modalities for both interdigital neuritis and tarsal tunnel syndrome have high failure rates and can lead to complications. These treatments typically address the inflamed nerve without identifying the cause of the inflammation. Current treatments interdigital neuritis include changes in shoes, padding, orthoses, injections of corticosteroids, injections of denatured alcohol and when all else fails, surgical excision. For tarsal tunnel syndrome, a variety of treatment options are used, often in combination to treat tarsal tunnel syndrome. These options include: rest, ice, nonsteroidal anti-inflammatory, immobilization, physical therapy, injected corticosteroid, orthotic devices, supportive shoes and surgical decompression of the nerve. Such methods of treating interdigital neuritis and/or tarsal tunnel syndrome each have uncertain success rates, significant limitations and the potential for complications
Changes in shoes: It is believed that a shoe that is too narrow in the forefoot will cause nerve irritation due to forefoot compression leading to interdigital neuritis. For this reason patients are recommended to change their shoes to a wider width to alleviate these compression forces. Unfortunately wearing wide shoes at all times is impractical for many due to their occupation and even when changes to wider shoes are made, interdigital neuritis may still persist. Furthermore, interdigital neuritis may even present in the absence of shoes entirely, becoming painful only when patients are barefoot.
Padding: Metatarsal pads are frequently applied to the shoe insole underneath the forefoot to separate the crowded metatarsals believed to be causing nerve inflammation. There is no standard thickness, size or placement of pad making reproducibility and accurate placement difficult if not impossible from shoe to shoe.
Orthoses: Orthoses are used to prevent or treat interdigital neuritis. For this purpose, orthoses providing support underneath the metatarsals are used to increase the intermetatarsal distance by reducing forefoot pronation and metatarsal hypermobility. There is no agreement whether non-custom orthoses, custom orthoses, anti-pronation or anti-supination orthoses are the most effective for patients having neuroma and orthoses cannot be worn in all styles of shoes. Similarly, orthotic devices and supportive shoes are used for tarsal tunnel syndrome, with the goal of maintaining the arch and limiting excessive motion that can cause compression of the nerves in the tarsal tunnel.
Injections: There are two types of injection for interdigital neuroma and two types of injection for tarsal tunnel syndrome. The first, for both interdigital neuritis and tarsal tunnel, is a corticosteroid injection which is designed to reduce nerve inflammation. The second injection for interdigital neuritis is a sclerosing or denatured alcohol injection to destroy the nerve at the point of inflammation. The second injection for tarsal tunnel syndrome is a local anesthetic simply to provide pain relief. Potential complications for both methods include infection and allergic reaction. In the case of corticosteroids, there is also the possibility of skin or muscle atrophy and pigment changes in the skin.
Surgery: In cases when conservative measures fail, surgical resection of the inflamed nerve is undertaken to treat interdigital neuritis. This surgery carries a risk of formation of an amputation stump following resection of the nerve. Similarly, when conservative treatment fails, surgical decompression of the tibial nerve at the tarsal tunnel is used to treat tarsal tunnel syndrome. During surgery the skin is incised and the tarsal tunnel is opened. The tibial nerve is identified and followed into the foot, where all compression points are released. In addition to the potential for infection, painful scars at the incision site also can form.